Passage doors for motor vehicle climate control systems have long been used to direct the flow of air through various passages of the climate control system as selected to achieve a specific climate state. As the popularity of vans and other vehicles with larger-than-standard passenger compartments has grown, there has been a concomitant use of larger air passages within the climate control system to accommodate larger air flow through the system in order to more efficiently control the climate of the larger passenger compartment. As the size and the cross-sectional area of the air passages increases, however, it takes more effort to move the door controlling flow through that passage, since the fluid pressure against which the door operates also increases with the increase in cross-sectional area.
The present invention eliminates the need to provide bigger, heavier, and more expensive mechanisms to open the door against the greater force caused by air pressure present in larger passages by providing a dual door assembly. In the dual blend door assembly of the present invention, the main door which controls the flow of fluid through a passage of the motor vehicle climate control system is provided with a smaller, inner door within the main door. The invention provides means to open the smaller, inner door, thus uncovering an opening within the main door, prior to attempting to move the larger main door itself. Since the cross-sectional area of the inner door is necessarily smaller than the cross-sectional area of the main door, the force against which the inner door operates is smaller than the force on the entire door assembly and less effort must be exerted by a control system to open this inner door. Of course, once the inner door exposes the opening within the main door, air pressure on either side of the main door begins to equalize and less effort is then needed to open the main door itself. By this operation, the present invention allows opening of the door assembly with less effort than would be required to open a unitary door, thus allowing more efficient operation of the door assembly. Additionally, the coaxial relationship between the inner door and the main door provides a more simple and efficient design of this dual blend door assembly.
In contrast, the flap valve of German Patent No. 2,015,065 discloses an auxiliary flap 4 which is located in the center of main flap 3, and is thus not coaxial therewith. As a result, the flap valve of German Patent 2,015,065 is provided with an actuating arm 6 which opens auxiliary flap 4 in a direction perpendicular from the plane of main flap 3, with subsequent continued retraction of the auxiliary flap 4 by the actuating arm eventually pivoting main flap 3 around pivot shaft 5. Further, this German patent is not intended for a motor vehicle climate control system and is, therefore, of minor relevance to claims of the present invention directed to a dual blend door assembly for such a motor vehicle climate control system.
German Patent 2,604,432 discloses a two-part butterfly valve in which the two moving portions are mounted along side each other rather than providing a design similar to the present invention in which a moving inner door is mounted within the larger, moving main door, with both the main door and inner door being mounted coaxially and substantially coextensively with a pivot shaft.